Bandstop filters are used in microwave systems to remove unwanted signals over a specific frequency range while passing signals with frequencies that fall outside of that range. Microwave bandstop filters can be used to reflect or absorb unwanted signals in a microwave system. These unwanted signals can originate from co-site or externally generated interference as well as nonlinear components under high-power excitation in the system. For example, a traditional microwave bandstop filter can be composed of resonators coupled to a through line with quarter-wavelength admittance inverters between each resonator. This bandstop filter topology can produce a symmetric notch frequency response and meet a wide variety of practical specifications. However, when the traditional microwave bandstop filter topology is used for high-order filters, the total through-line length becomes long.
Switched bandstop filters implement a reconfigurable frequency response at the front-end of an RF system that allows it to receive or reject a specific frequency band on demand. The conventional switched-bandstop-filter configuration is comprised of switches in conjunction with a bandstop filter and bypass transmission line in parallel. The switches route an RF signal to the internal direct path for all-pass mode or to the filter path to engage the bandstop filter. In this approach, the RF signal experiences significant insertion loss from the switches.
In the case of reconfigurable or frequency-agile systems, it is often a requirement that each bandstop filter have bypass capability. Using two signal-routing radio frequency (RF) switches for every bandstop filter typically results in considerable insertion loss when multiple switched filters are cascaded due to the losses of the switches.
Features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.